DESCRIPTION: This application is a request for a new investigator RO1 to examine sibling-effects on antisocial behavior. Despite an emerging literature that has suggested that siblings may exert pronounced and unique effects on the development of antisocial behavior, empirical efforts to document sibling effects have lagged behind the identification of parental and peer influences. The proposed project is an attempt to fill this gap by focusing on the processes by which siblings may train, reinforce, and promote each other's initiation and escalation of antisocial behavior, especially during adolescence as the peak period for engagement in deviant behavior. The overall goal of this project is to address detailed questions about sibling effects on antisocial behavior by using two interrelated study samples especially well-suited to this purpose. These longitudinal data sets, the Iowa Youth and Families Project and the Iowa Single Parent Project, have assessed over 600 sibling pairs over multiple time points from early to late adolescence, including videotaped records of sibling interaction and independent reports of antisocial behavior at every assessment period. Through the application of well-developed coding systems designed to study microanalytic social processes to the collected videotapes of sibling interaction the project will pursue five specific aims: (1) to investigate coercive or negative reinforcement cycles in sibling interactions hypothesized to condition risk for antisocial or delinquent behavior (2) to investigate the influence of sibling approval or positive reinforcement of deviant actions or verbalizations that may function as conditional factors for the initiation or maintenance for antisocial behavior; (3) to clarify which social processes between siblings are salient for the development of antisocial behavior at different developmental periods (early to latter adolescence); (4) to test if the salient social processes between siblings differ systematically according to gender compositions and (5) to determine the degree to which parenting practices affect social processes in the sibling relationship that either increase or decrease risk for adolescent antisocial behavior as well as the extent to which sibling influence is independent of parenting behavior. Both regression and latent growth curve models will be applied to reveal conditional associations between sibling interaction and antisocial behavior over time and sequential statistics will be used to isolate hypothesized behavioral exchanges between siblings. Such detailed examinations of specific intersectional patterns between siblings may identify social processes that act as conditional factors that can increase or diminish the likelihood engagement in serious antisocial behavior during adolescence.